This invention relates to electrostatographic reproduction machines, and more particularly to a liquid immersion development (LID) electrophotographic reproduction machine having a highly effective high differential air pressure assisted image blotting device.
Liquid electrophotographic reproduction machines are well known, and generally each include a development system that utilizes a liquid developer material typically having about 2 percent by weight of fine solid particulate toner material dispersed in a liquid carrier. The liquid carrier is typically a hydrocarbon. In the electrophotographic process of such a machine, a latent image formed on an image bearing member or photoreceptor is developed with the liquid developer material. The developed image on the photoreceptor typically contains about 12 percent by weight of particulate toner in liquid hydrocarbon carrier. To improve the quality of transfer of the developed image to a receiver, the image is conditioned so as to increase the percent solids of the liquid developer forming the image to about 25 percent. Such conditioning is achieved by removing excess hydrocarbon liquid from the developed liquid image. However, such removal must be carried out in a manner that results in minimum degradation of the toner particles forming the liquid image. The conditioned image is then subsequently transferred to a receiver which may be an intermediate transfer belt and then to a recording or copy sheet for fusing to form a hard copy.
Liquid electrophotographic reproduction machines as such can produce single color images or multicolor images on such a recording or copy sheet. The quality or acceptability of a color copy produced as such is ordinarily a function on how the human eye and mind receives and perceives the colors of the original and compares it to the colors of the copy. The human eye has three color receptors that sense red light, green light, and blue light. These colors are known as the three primary colors of light. These colors can be reproduced by one of two methods, additive color mixing and subtractive color mixing, depending on the way the colored object emits or reflects light.
In the method of additive color mixing, light of the three primary colors is projected onto a white screen and mixed together to create various colors. A well known exemplary device that uses the additive color method is the color television. In the subtractive color method, colors are created from the three colors yellow, magenta and cyan, that are complementary to the three primary colors. The method involves progressively subtracting light from white light. Examples of subtractive color mixing are color photography and color reproduction. Also, it has been found that electrophotographic reproduction machines are capable of building up a full subtractive color image from cyan, magenta, yellow and black. They can produce a subtractive color image by one of three methods.
One method is to transfer the developed image of each color on an intermediary, such as a belt or drum, then transferring all the images superimposed on each other on a sheet of copy paper.
A second method involves developing and transferring an image onto a sheet of copy paper, then superimposing a second and subsequent images onto the same sheet of copy paper. Typically an image processing system using this method can produce a first color image by developing that color image on a photoconductive surface, transferring the image onto a sheet of copy paper, and then similarly and sequentially producing and superimposing a second, and subsequent images onto the same sheet of copy paper.
A third method utilizes what is referred to as a Recharge, Expose, and Develop or REaD process. In this process, the light reflected from the original is first converted into an electrical signal by a raster input scanner (RIS), subjected to image processing, then reconverted into a light, pixel by pixel, by a raster output scanner (ROS) which exposes the charged photoconductive surface to record a latent image thereon corresponding to the subtractive color of one of the colors of the appropriately colored toner particles at a first development station. The photoconductive surface with the developed image thereon is recharged and re-exposed to record the latent image thereon corresponding to the subtractive primary of another color of the original. This latent image is developed with appropriately colored toner. This process (REaD) is repeated until all the different color toner layers are deposited in superimposed registration with one another on the photoconductive surface. The multi-layered toner image is transferred from the photoconductive surface to a sheet of copy paper. Thereafter, the toner image is fused to the sheet of copy paper to form a color copy of the original.
Liquid developer typically contains about 2 percent by weight of fine solid particulate toner material that is dispersed in a carrier liquid, such as a hydrocarbon. The developed image on the imaging member or photoreceptor ordinarily contains about 12 weight percent of particulate toner material or particles in the hydrocarbon carrier liquid. Conditioning such an image therefore includes increasing the percent solids of the image by removing carrier liquid from the image while preventing the solid toner particles from leaving the image, and of electrostatically compressing or compacting the toner particles in order to physically stabilize the image, and produce a clear, high resolution image.
Such conditioning must however be achieved without disturbing the toner image, and in such a manner as to prevent toner particles from entering the carrier liquid removal device. In addition, the carrier liquid removal device must also remain clean and free of toner particles so as to prevent it from thereafter contaminating a subsequent image with embedded toner particles, and so as to ensure an extended useful life for the device.
Various techniques and devices including blotter rolls or rollers have been devised for conditioning the liquid developer image by removing carrier liquid from the image as discussed above. Such blotter rolls may include a vacuum removal system and an electrical bias applied thereto in order to assist the removal process. The following references may be relevant to various aspects of the present invention.
U.S. Pat. No. 4,286,039 discloses an image forming apparatus comprising a deformable polyurethane roller, which may be a squeegee roller or blotting roller which is biased by a potential having a sign the same as the sign of the charged toner particles in a liquid developer. The bias on the polyurethane roller is such that it prevents streaking, smearing, tailing or distortion of the developed electrostatic image and removes much of the carrier liquid of the liquid developer from the surface of the photoconductor.
U.S. Pat. No. 4,985,733 issued Jan. 15, 1991, to Kurotori et. al. discloses a liquid toner copying machine including a non-thermal image conditioning apparatus comprising an elastic blotter roll and an elastic backup roller for bringing a liquid toner image carrying sheet into contact with the blotter roll.
U.S. Pat. No. 5,136,334 issued Aug. 4, 1992, to Camis et. al. discloses a liquid toner image conditioning apparatus including a heated inner core connected to a source of AC or DC bias, and having a smooth outer surface made of a soft elastomeric material.
U.S. Pat. No. 5,332,642, having a common assignee as the present application, discloses a porous roller for increasing the solids content of an image formed from a liquid developer. The liquid dispersant absorbed through the roller is vacuumed out through a central cavity of the roller. The roller core and/or the absorbent material formed around the core may be biased with the same charge as the toner so that the toner is repelled from the roller while the dispersant is absorbed.
Each of the above example references includes a currently conventional blotter roller having a rigid core, and at least an absorbent layer over such core with the blotter roll mounted in a LID machine to directly contact a liquid toner image on the image bearing member of the reproduction machine. A conventional blotting device assembly that includes such a blotter roll, often has an assisting vacuum source connected to the core of the blotter roll for vacuum-drawing carrier liquid from an image being conditioned, through and out of the blotter roll.
It has been found that conventional blotting assemblies or devices as such are ordinarily limited by their absorbency capacity and by a need to apply a non-image disturbing level of vacuum (usually a partial vacuum) with respect to the degree to which each can remove carrier liquid from an image being conditioned. Because the blotter roll in such a device is typically made of a thin wall, sintered metal tube, a force with which it can be loaded against the image being conditioned, is also limiting. This of course also limits the effective blotting results of the device. Furthermore, because vacuum is applied directly against the image being conditioned, there is understandably the risk of image disturbance, and of early blotter roll failure from toner particles being sucked from the image into the pores of the surface layer of the blotter roll. Another undesirable effect of applying vacuum directly against an image being conditioned by a blotter roll having pore and non-pore surface layer areas that contact the image, can be a non-uniform appearance in the image between areas thereof contacted by pore surface layer areas, and those contacted by non-pore surface layer areas of the blotter roll.
There is therefore a need for developing a LID image blotting method and apparatus for achieving highly effective, uniform and non-disturbing image blotting without the above cited limitations.